By ANTHONY BURGESS; Anthony Burgess's most recent novel is ''Any Old Iron.''

Published: October 15, 1989

First, profound obeisances to William Weaver, the marvel of whose translation I am able to confirm, having read much of Umberto Eco's new novel in the original. The mountain of information in it was piled up from sources in many languages and gathered through many centuries, and its characters are masters of such obscure and mystery-laden arts that it is dizzying in any language. Carrying the whole thing over from one to another must have been a monstrous task. Not an easy book, ''Foucault's Pendulum'' is an encyclopedic detective story about a search for the center of an ancient, still-living conspiracy of men who seek not merely power over the earth but the power of the earth itself, and who in the end draw their pursuers into a circle where discovery of the truth is lethal. It is not meant to be easy. But neither was ''The Name of the Rose,'' which became a best seller, even though one wonders how many people actually read all of it. ''Foucault's Pendulum'' will almost certainly become a best seller as well, and great are the rewards for those who actually manage to read it. For while it is not a novel in the strict sense of the word, it is a truly formidable gathering of information delivered playfully by a master manipulating his own invention - in effect, a long, erudite joke.

Mr. Eco heard all about the pendulum, which swings in the Conservatoire des Arts et Metiers in Paris, from Mario Salvadori, a professor of civil engineering and architecture at Columbia University, or so an article in the newspaper Corriere della Sera tells me. An extract from a letter by that learned man forms one of Mr. Eco's 120 chapter epigraphs. The pendulum was invented by Jean Bernard Leon Foucault (1819-68) to demonstrate the rotation of the earth. It seems harmless, the confirmation of a comforting permanence, but it turns sinister toward the end of Mr. Eco's novel. The novel as narration is put into the mouth of a character named Casaubon, who has written his doctoral thesis on the Knights Templar and, after a sojourn in Brazil, is back in Milan as a kind of Sam Spade of information. For a price, he will track anything down, but he already seems to know everything, except that he is named for the etiolated scholar of George Eliot's ''Middlemarch,'' who also knew everything, though it did him no good.

He is found useful by a firm of publishers, for which Jacopo Belbo, a commonsensical Piedmontese, works. Belbo's favorite comment on pretentiousness is ''Ma gavte la nata,'' which means something like ''take out the cork and let the wind blow away.'' For all that, Belbo earns a living in what is termed vanity publishing, which allows cranks and obsessives to see their work in print so long as they pay for it. His associate in publishing is one Diotallevi, whose obsession is the cabala and who insists that, although his forebears were not Jewish, he is, and that he has an ''exquisite Talmudic understanding.''

One of the cranks is a Colonel Ardenti, who believes he has discovered a coded message about a plot engineered by the Knights Templar. The Knights, a papal order of crusaders founded in the 12th century and officially disbanded by the Pope in the 14th, are apparently still around in some form or other. Their plot, aimed at taking over the whole world through the deployment of telluric energy (the fundamental powers of the planet, named for the Roman earth goddess Tellus), is the ultimate conspiracy.

The world, as we know, is full of conspiracy hunters. Sometimes the conspirators are the C.I.A., sometimes the makers of Coca-Cola, or all the Jews, all the Catholics. The intelligence officer in Evelyn Waugh's novel ''Sword of Honour,'' Colonel Grace-Groundling-Marchpole, believes that the Nazis and the Allies are in conspiracy. The ultimate conspiracy synthesizes all possible conspiracies - il complotto dei complotti - and one wonders what precisely they are complotting against. No matter. A plot is a structure, a semiotic fabrication. Umberto Eco is a professor of semiotics, a grand master of codes, signs and hidden meanings.

The triumvirate of publishers - Diotallevi, Belbo and Casaubon - decide, as a game, to feed all the hermetic plots that ever were into their computer, which is named Abulafia after the medieval Jewish cabalistic philosopher. The disgorgements will go beyond crazy Colonel Ardenti's ultimate conspiracy: the cosmic plan will embrace opposites. It will also provide better interpretations than orthodox history ever did of certain past events. For instance, the Knights Templar may have been disbanded for homosexuality, but their kissing of each other's fundaments had nothing to do with unlawful love. They were honoring the great serpent Kundalini, which ''throbs gently, binding heavy bodies to lighter bodies. Like a vortex or a whirlpool, like the first half of the syllable om.'' A Christian body evidently had access to ancient Indian lore.